Can’t decide between guppies or mollies for your freshwater tank? These two popular livebearers are beautiful, easy to keep, and breed like crazy—but they have distinct personalities, care needs, and habitat preferences. If you’re planning a long-term, low-maintenance tank where either fish can thrive, Aquaponics 4 You shows you how to set up a natural system that balances waste, grows plants, and keeps your water clean—automatically.
Quick Comparison: Guppies vs Mollies
| Feature | Guppies | Mollies |
|---|---|---|
| Size | 1.5–2.5 inches | 3–4.5 inches |
| Temperament | Peaceful, playful | Peaceful but more dominant |
| Water Preference | Freshwater | Fresh or brackish water |
| Tank Size | 10 gallons and up | 20 gallons and up |
| Breeding | Very prolific | Very prolific |
| Care Level | Beginner | Beginner to Intermediate |
| Lifespan | 2–3 years | 3–5 years |
Overview of Guppies
Guppies (Poecilia reticulata) are among the most popular beginner fish in the hobby. They’re small, colorful, and endlessly entertaining. Guppies come in a variety of tail shapes and colors, and their playful nature makes them great for community tanks.
Key Traits:
- Extremely colorful, especially males
- Fast swimmers and social in groups
- Easy to breed—females give birth every 30 days
- Prefer slightly hard, alkaline water
- Great in planted tanks
Overview of Mollies
Mollies (Poecilia sphenops and hybrids) are a bit larger and more robust than guppies. They come in several varieties—balloon mollies, sailfin mollies, black mollies—and they’re known for their graceful swimming and tolerance to varying water conditions, even brackish water.
Key Traits:
- Hardy and adaptable to fresh or brackish water
- Larger size requires more space
- Also prolific breeders, but slower than guppies
- May show dominant behavior in small tanks
- Thrive in planted tanks with algae and biofilm
Mid-Article CTA: Want a Tank That Practically Maintains Itself?
Whether you choose guppies or mollies, they both produce waste that fuels plant growth in a properly balanced system. Aquaponics 4 You shows you how to use that waste to grow herbs, clean your water, and reduce water changes—saving time and money while keeping your fish healthy.
Water Parameters: What Do They Need?
Guppies:
- Temperature: 74–82°F
- pH: 7.0–8.2
- Hardness: Moderate to hard
Mollies:
- Temperature: 75–80°F
- pH: 7.5–8.5
- Hardness: Hard to very hard
- Can tolerate brackish water (small salt amounts)
Note: If your tap water is naturally soft, guppies may be easier to maintain unless you’re willing to buffer the water or use additives for mollies.
Breeding Behavior
Guppies:
- Breed readily and often
- Males constantly court females—ratio of 1 male to 2+ females is best
- Fry are small and often eaten by adults if not separated
Mollies:
- Also livebearers, but have fewer, larger fry
- More likely to tolerate tankmates than eat fry
- Need space and good nutrition for successful breeding
Temperament and Tank Mates
Guppies:
Very peaceful. Ideal tankmates include:
- Tetras
- Corydoras
- Small rasboras
- Snails and shrimp (with caution)
Mollies:
Generally peaceful but can become pushy in small tanks. Suitable companions include:
- Platies
- Swordtails
- Larger tetras
- Peaceful gouramis
Warning: Avoid housing guppies or mollies with fin-nippers like barbs or aggressive cichlids.
Diet Comparison
Guppies:
- Omnivores—enjoy flakes, micro pellets, baby brine shrimp
- Prefer smaller foods due to size
- Need some vegetable matter (e.g., spirulina flakes)
Mollies:
- Primarily herbivorous but will eat anything
- Love algae and biofilm—great natural cleaners
- Benefit from blanched veggies and algae wafers
Health & Lifespan
Both species are hardy but have different health concerns:
Guppies:
- Prone to fin rot, especially from poor water quality
- Shorter lifespan (2–3 years)
- Overbreeding can lead to stress in females
Mollies:
- May develop “shimmies” if kept in soft water
- Can live 3–5 years with proper care
- Need more frequent tank cleanings due to size and waste
Which Fish Is Right for You?
| Choose Guppies If You… | Choose Mollies If You… |
|---|---|
| Want a colorful, small, beginner-friendly fish | Have a larger tank and want robust, adaptable fish |
| Prefer freshwater only with little adjustment | Can handle brackish or harder water needs |
| Enjoy frequent baby fish (fry) and breeding | Want fish that help clean algae and debris |
| Have a peaceful community setup | Like fish with personality and bolder behavior |
Can You Keep Guppies and Mollies Together?
Yes, guppies and mollies can coexist in the same tank as long as you meet these conditions:
- Minimum tank size: 20 gallons
- Maintain hard, alkaline water (pH 7.5+)
- Provide plenty of plants and hiding places
- Feed both plant-based and protein foods
Mollies may be a bit dominant, so monitor interactions closely. Avoid keeping too many males of either species in a small tank.
Final Thoughts: Guppies vs Mollies
Both guppies and mollies are excellent additions to a community tank. Guppies are better suited for smaller, peaceful setups and those just starting out. Mollies offer more size, bold behavior, and algae-cleaning benefits—but need more room and harder water to thrive. If your tank is large enough and your water matches their needs, there’s no reason you can’t enjoy both!
Final CTA: Ready to Build a Healthy, Self-Sustaining Tank for Guppies or Mollies?
Why fight algae and poor water quality when your fish can help balance the tank? Aquaponics 4 You teaches you how to use fish waste to feed plants, reduce maintenance, and create a closed-loop system where guppies or mollies thrive. Download your guide now and transform your fishkeeping game today.